Chirality and Magnetocaloricity in GdFeTeO6 as Compared to GdGaTeO6

Abstract

GdFeTeO6 and GdGaTeO6 have been prepared and their structures refined by the Rietveld method. Both are superstructures of the rosiaite type (space group ). Their thermodynamic properties have been investigated by means of magnetization M and specific heat Cp measurements, evidencing the formation of the long-range antiferromagnetic order at TN = 2.4 K in the former compound and paramagnetic behavior down to 2 K in the latter compound. Large magnetocaloric effect allows considering GdFeTeO6 for the magnetic refrigeration at liquid hydrogen stage. Density functional theory calculations produce estimations of leading Gd–Gd, Gd–Fe and Fe–Fe interactions suggesting unique chiral 120° magnetic structure of Fe3+ (S = 5/2) moments and Gd3+ (J = 7/2) moments rotating in opposite directions (clockwise/anticlockwise) within weakly coupled layers of the rosiaite type crystal structure.

Successive short- and long-range magnetic ordering in rosiaite-type CoGeTeO6 prepared by ion-exchange reaction

“…It has been shown in ref. 21 that the only solution compatible with the observed properties is the 120°structure of Fe 3+ moments within iron-tellurium layers (say, clockwise) and the 120°structure of Gd 3+ moments within gadolinium layers (say, anticlockwise).…”

“…15 One more type of rosiaite-related phase has the formula R 3+ M 3+ TeO 6 , where R = rare earth or Bi, and M = Cr, Mn or Fe. [16][17][18][19][20][21][22] Of special interest is rosiaite-type GdFeTeO 6 since both rare-earth and transition metals possess the largest spin moments among the corresponding magnetic rows. GdFeTeO 6 and its iron-free counterpart GdGaTeO 6 crystallize in a superstructure of the rosiaite (space group P3 ˉ1c) due to the doubling of the c parameter since either Fe/Te or Ga/Te alternate along the principal axes.…”

“…No long-range magnetic ordering was found in GdGaTeO 6 down to 2 K while GdFeTeO 6 exhibited long-range ordering at T N = 2.4 K. GdFeTeO 6 possesses excellent magnetocaloric properties, which makes it promising for the working body of low-temperature magnetic refrigerators. 21 The absence of the magnetic order in GdGaTeO 6 points to the weakness of the Gd-Gd interactions. Since no long-range order has been detected in LaFeTeO 6 , the interlayer Fe-Fe interactions are also weak.…”

“…1c). [16][17][18][19][20][21] Attempts to directly prepare MGeTeO 6 (M = Co, Ni, Cu, Pd) failed resulting in complex mixtures with no sign of any rosiaite-related phases. 14 However, using ion exchange reactions under relatively mild conditions, we succeeded in preparing CoGeTeO 6 .…”

Triangular Magnet Emergent from Noncentrosymmetric Sr0.94Mn0.86Te1.14O6 Single Crystals

“…Two of them are superstructures of the rosiaite (PbSb 2 O 6 ) structure-type (centrosymmetric space group P 31̅ m ) with all cations in octahedral coordination but differ in the M/Te ordering pattern. In AMTeO 6 (A = rare earth or Bi; M = Cr, − Mn, , or Fe ,, ), M and Te alternate along the principal axis. This results in doubling the cell edge c but the structure retains the inversion center, space group being P 31̅ c (or P 2 1 / c for BiMnTeO 6 , distorted by the Jahn–Teller effect).…”